1. Field of the Invention
The present invention relates to color processing according to the viewing conditions of an image.
2. Description of the Related Art
Along with the prevalence of devices which handle color images, opportunities to display an image captured by a digital camera on a color monitor or print such an image by a color printer have increased. In this case, since the range of representable colors (to be referred to as a color gamut, hereinafter) differs in each device that handles color images, color processing for absorbing the differences between the color gamuts of devices is necessary. This color processing is performed in a device-independent color space such as a CIELab color space. Recently, however, the color appearance space of a color appearance model (e.g., CIECAM02) that models the human visual characteristics with a higher accuracy than conventional color spaces is beginning to be utilized.
A color appearance model (CAM, hereinafter) converts a CIEXYZ value into a color value of a color appearance space by using an ambient light parameter according to the viewing condition of a color image. The viewing condition includes the color temperature and intensity of illumination of the light source of an environment in which a color image is viewed. Based on the measurement data of the light source or the like, the CIEXYZ value or adaptation luminance of a white point as an ambient light parameter of the CAM is calculated. That is, in order to obtain a color image most suitable for a specific viewing environment in which the image is viewed, color processing is performed by setting an accurate ambient light parameter according to that viewing condition.
However, since an image printed by a color printer, a mobile PC, or the like can be portable, a color image is not always viewed in the viewing environment corresponding to the ambient light parameter of color processing. In other words, a color image is often viewed in various environments with different types of light sources such as indoor and outdoor or a fluorescent light and an incandescent light. Therefore, even when a color image which underwent color processing based on the ambient light parameter adapted to a specific viewing environment is printed or displayed, the original color of the color image is not represented in an environment having a different viewing condition.